The present invention relates to feedback controller apparatus and process control systems, and more particularly relates to a controller apparatus capable of self-tuning control parameters such as proportional-integral-derivative (PID) control parameters and a process control system using a plurality of such self-tuning controller apparatus.
Conventionally, an operator has manually perform the tuning of PID control parameters in a PID controller while observing variations in a controlled variable. In the point of view of the control theory, on the other hand, there have been numbers of proposals as to a system in which an identifying test signal is applied to a process (or controlled object, controlled system or the like) to identify the dynamic characteristics of the process so that a control parameter is tuned to an optimum value on the basis of the result of identification.
Further, as a heuristic method (expert method) in which a control parameter tuning is performed while observing a controlled variable response pattern or shape, known is a method disclosed in JP-A-62-108306. According to this method, an actual response pattern is compared with a plurality of reference response patterns to find a reference response pattern which matches the actual response pattern and an optimum rule is selected among a plurality of adjustment rules corresponding to the matched reference response pattern in accordance with the actual response pattern or the transient tendency of the actual response pattern to thereby correct PID control parameters. As the method of this kind, further known is that disclosed in U.S. Pat. No. 4,602,326. Further, U.S. Pat. No. 4,903,192 filed Apr. 1, 1988 relates to a PID controller system.